Dense wavelength division multiplexing (D-WDM) is promising in future information networks to increase the communication bandwidth. One of the most crucial components for effective D-WDM is a fast tunable optical filter. Such tunable optical filters should be able to filter out desired wavelengths quickly, finely (narrow spectral bandwidth) and over a broad tuning range to cover the erbium-doped fiber amplifier (EDFP) passband (from about 1530 nm-1570 nm).
The acousto-optic tunable filter is currently the most commonly utilized for D-WDM. However, the spectral bandwidth of heretofore known acousto-optic tunable filters is broad (several nm for an interaction length of 1 cm) thus causing serious crosstalk problems due to sidelobes. This limits the number of wavelength channels available in D-WDM at a development stage where increasingly faster tunable spectral filters permitting a larger number of wavelength channels within the EDFA passband are demanded. Thus, while acousto-optic devices are promising for this application because they provide fast wavelength tuning (on the order of a few micro seconds), wide tuning range (greater than 100 nm) and simultaneous and independent selection of many wavelengths, further improvement could still be utilized.